共查询到15条相似文献,搜索用时 78 毫秒
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电磁热效应对T7钢的裂纹止裂 总被引:4,自引:3,他引:1
利用电磁热效应原理,在自制的ZL0-1型超强度脉冲电流以发生装置上,对T7钢的纹止裂效果进行了初步研究。表明:对试件实施放电瞬间,在裂纹尖端处形成焊口使裂纹尖端的同蓄半径增大,达到抑制裂纹扩展的目的。同时:对裂纹尖端热影响区的组织进行了分析,并讨论了因快速加热和冷却作用所获得细小淬火马氏体组织及热压应力和相变压应力对止效果的影响。 相似文献
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利用自行研制的ZL-2型超强脉冲电流发生装置对带有单边裂纹的Al-Mg合金试件进行电磁热止裂实验,并对放电前后裂纹尖端的微观组织进行对比分析;采用热-电-结构耦合的数值分析方法求得放电后试件的电流密度场、温度场及热应力场;从理论上计算放电后的电热应力强度因子。结果表明:放电电压对止裂效果存在最优值;在适当的强脉冲电流作用下,裂纹尖端在小范围内被瞬间强化加热,随后在极大的热压应力作用下快速冷却,组织发生明显变化,晶粒得到细化,并围绕裂纹尖端形成等值压缩热应力,对裂纹尖端有"夹紧"作用,进而阻止裂纹扩展。 相似文献
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9Cr2凸模半埋藏疲劳裂纹电磁热止裂的实验与模拟研究 总被引:1,自引:0,他引:1
电磁热效应止裂技术的发展为金属模具中半埋藏裂纹的止裂问题提供了有效的解决途径。文章采用实验和数值模拟分析方法研究了对带有半埋藏裂纹的9Cr2凸模进行脉冲放电,实施电磁热止裂。实验结果表明,脉冲放电瞬时半埋藏裂纹尖端附近金属温升超过熔点,裂尖熔化形成焊口,并且由于裂纹是半埋藏状态,熔化的金属在裂尖处形成堆焊,其周围发生有利于遏制裂纹扩展的组织细化,有效地遏制了裂纹的扩展;数值模拟结果表明,脉冲放电瞬间,裂纹尖端附近很小的区域内,温度和温度梯度变化极大,裂纹尖端金属迅速熔化,导致半埋藏裂纹尖端曲率半径增加几个数量级,数值模拟分析结果与实验结果相吻合。 相似文献
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建立带有单边裂纹的无限大金属薄板模型,给出脉冲放电瞬间的温度场,应用一维条件下的热弹塑性理论,导出了单边裂纹金属构件电磁热止裂后的一维残余应力解;对带有单边裂纹的导电薄板脉冲放电后裂纹尖端产生的残余应力进行数值分析,理论与数值分析结果基本吻合;对40CrNiMo试件的残余应力超声波无损检测发现,止裂后残余应力变大。研究表明,在对带有单边裂纹的导电薄板进行电磁热止裂时,裂纹尖端周围温度急剧升高,使得裂纹尖端受热膨胀,由于裂尖受到周围材料的刚性约束,在受热和冷却过程中会残留一个压缩塑性应变,其产生的残余应力可有效的抑制裂纹扩展。 相似文献
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采用ANSYS分析软件对45钢焊接接头电磁热强化过程进行了数值仿真,并对其强化后的温度场和残余应力场进行了分析.结果表明,电磁热强化使焊接接头内部裂纹尖端钝化,减少了应力集中,焊接裂纹尖端形成了3向残余压应力场.通过ZL-2型脉冲放电装置对45钢焊接接头进行了电磁热强化试验,并对其进行了强化前后力学性能对比分析.经过脉冲放电强化后的焊接接头抗拉强度和断后伸长率均有所提高,其力学性能得到了改善.数值分析和试验研究均证实了电磁热强化技术应用到焊接领域的可行性. 相似文献
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《Science & Technology of Welding & Joining》2013,18(6):478-484
AbstractThe effect of the distance between loading points on a long brittle crack arrest behaviour was investigated in the ultrawide duplex ESSO tests. The effect of loading conditions was also analysed. Arrest of a long brittle crack was more facilitated in the tests with a distance between loading points of 5 m than in those with 10 m. A load drop was larger in the tests with a loading point distance of 5 m than in those with 10 m. If the specimen length is 6·8 m or more, or the distance between loading points are 10 m or more in the ultrawide duplex ESSO test, the effect of the unloading stress wave on the dynamic stress intensity factor of a crack penetrating into the test plate becomes negligible, within the range of brittle crack propagation rate between 500 and 800 m s?1. 相似文献
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Tsunehisa Handa Satoshi Igi Kenji Oi Kimihiro Nishimura Hisakazu Tajika Tetsuya Tagawa 《Welding International》2013,27(7):460-468
ABSTRACTBrittle crack arrestability of the heavy gauge steel plates for shipbuilding is now an important issue for the recent mega container ships. In the present work, the brittle crack arrestability of the steel plate with different toughness distributions in thickness is examined in ultra-wide duplex ESSO tests. It is examined whether a running long brittle crack arrests or not in flat temperature condition in ultra-wide duplex ESSO test that are harder mechanical conditions similar to an actual ship hull condition. Test temperatures are selected at which arrest toughness, Kca, evaluated by temperature gradient type standard ESSO test is the same for two test plates. The steel plate with higher toughness in mid-thickness (t/2) than that in quarter thickness (t/4) could arrest a running long brittle crack although the plate with lower toughness in mid-thickness than that in quarter thickness could not arrest it. The typical split-nail shape appeared at the arrested crack front in the plate with higher toughness in mid-thickness than that in quarter thickness. The numerical analyses also demonstrate that the local stress intensity factor at the arrested crack tip is changing sensitively to the crack front shape. It suggests that the higher brittle crack arrestability appears due to the split-nail shape of the arrested crack front enhanced by the inhomogeneous toughness in thickness. 相似文献